I have Mi 8SE, the suite doesn't work, how to backup before update?

[TheNewbie]

I've purchased my phone from Chinese vendor and it came unlocked. I have no clue how to update to MIUI 10, the instructions here are very vague and are not newbie friendly. That doesn't matter, I'll try with scattered information, but how can I backup all my media files? The MI suite doesn't work, says I have to update my device first.